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Refrigerator

This is a new door.
I will explain why. It is simple: I lost the other door.

The door looks shiny because it is covered in aluminum foil. Now this stunt is hard to explain: It is caused by Russia. The refer door has some EMP shielding, and is always secured with two copper straps. I will not discuss Electromagnetic Pulses here. This is about the refrigerator.

I have the copper braid because, as I said, I lost a door once. I did not have both stupid little buttons turned closed. I got in a hurry and thought a partial "little" turn was good enough. Now, if the door comes off, I can hopefully see it swinging in the left rear view side mirror, and I can pull over and secure it. The doors do not cost much, but I do not want to be liable for detached flying projectiles. Not to mention serious damage to following behind vehicles. Or, God forbid, hurting someone.



The cheap wooden support from the factory under the refrigerator is coated in roofing paint, and then coated in aluminum. It now is water proof. Easier to keep clean too.

This was to become important a year later in a violent rain storm. Forty mile an hour winds were blowing rain horizontally through the vent. Fortunately, rain water did no damage under the refrigerator; It was water resistant. Water came in the door vents, did not pool much under the refrigerator, and flowed over the aluminum flooring, to the vinal floor inside the coach. I had a mysterious amount of water on the hall way floor in front of the refrigerator. But luckily no damage.



I can increase efficiency with a draft fan. 12 volt fan, 160mA. I used a couple of diodes, plus the transistor junction, to further reduce the voltage to less than 11 volts. The fan will be exposed to a lot of heat, and I do not want it taxed. The fan is supper quiet, and I can not hear it inside.











There is a more serious issue than ducting air.

Here is the "Board" for the refrigerator. Dometic has made a mistake on its design. It is an incredible story. I did not see the problem for years:
Inside on the control buttons there is a push button for "Automatic" and "Manual".
It is a familiar button on all Dometics. The button was designed to automatically select between Gas or 120AC electric. But the button also, by mistake or bad design, disables all temperature controls. As an unfortunate consequence, temperature control fails, and the temperature goes to max cold. It is true! WTF.

Refrigerator temperature

In the lower refrigerator section, not the top freezer, food would freeze, and drinks would freeze. The temperature of 33F degrees is for the refrigerator section, not the freezer. Many times vegetables in the lower bins would be frozen solid. WTF. No adjusting the temperature sensor up and down on the fins would help. I never knew it was a manufacturing design flaw on the board.

I fought the -10 degree ice in the freezer for years, but I had no way to know where the problem was, until I installed an indicator to tell me when the refrigerator was on. Only then I knew that it was a problem of the refrigerator never shutting off. The refrigerator runs so quiet. It is a problem of all Dometics of my vintage that are Two-Ways. I do not know about the Three-Ways. Inexcusable!




Getting back to the fan...


To install the fan, I have to know how the board works. I do not want a switch to turn onn the fan - The board will turn it on. The board will automatically turn on the fan when the refrigerator is onn.
There probably is enough current capability onboard that runs the solenoid. I could simple hook it to the solenoid. But no. I choose not to disturb the original board design. I will be gentle, and not load anything. I will use a bipolar transistor as an auxillary power switch external of the board.

The solenoid should have a reflex spike diode somewhere, which I do not see. But proper design of the board is not my concern. Instead, I will supply my own protection on the base.



Plenty of room under the pop out trim panel at the top of the frig. Just drilled a hole in the plastic, and inserted the LED. Easy-Peasy.



The red LED comes on when there is a flame.



The refrigerator vent.



Placed the fan at the top of the refrigerator vent. Fan only comes on when there is a flame.



I have calculated how much it costs me to make ice. It is not much, but it is far more convenient to use bulk ice, whether or not I make it. That is because it never melts. Found this food bin on Amazon.


Here are the two bins side by side: the old original opaque white, and the new clear. They are almost direct replacements - but not quite!


Both refrigerator and freezer doors are shown open. The freezer door shelves, or door bins, hit the new clear bin, but not the old white bins.
Two solutions:
1) put a white in freezer, and a clear in refrigerator.
2) remove a freezer shelf. They easily slip out. I can not imagine what they are used for anyway. Especially the wierd looking one on the left. Maybe dispenses business cards.


The refrigerator freezer door shelves hit the new bin. By not much, perhaps 1/4 inch, but the shelves do hit. Freezer works OK with one of the opaque whites.





My Dometic DM2652 uses propane gas at 1500 Btu/Hr, 440 Watts
(About 36,000 Btu/day 648,000 BTU/30lb bottle, 18 days, 1.6 lb/day, $1.33/day, 5.55cents/hr)

My Dometic uses 120 VAC 3.7 Amps, 444 Watts
(11.9cents/kWhr, .444kW x 11.9cents/kWh=5.3cents/hr)

A Three-Way uses 12v DC and can not be compared due to less cooling capacity.


If the efficiency is designed properly, all heat sources in an absorbtion refrigerator should be the same watts. And they are: 440 Watts. (However, Three-Ways with a 12v source can not deliver the high amperages, so the cooling capacity is reduced out of necessity due to wiring physics.)

Modern absorbtion refrigerators, I understand, use 135 Watts. And therefor, my Domitic is way out of line, is totally unreasonable, and should be scraped. Someday, I will replace it with a Compressor type that uses only 50 Watts, and I will be done with the flame.
There are two problems with this idea:
1) There is nothing wrong with the present refrigerator. In fact, it cools very well.
2) The present refrigerator is cheap to operate. Inefficient as it is, I can not complain about the cost.



Getting back to the big problem...

Here is the problem with the Dometic "Non-Recall":
For several hours my wife and I were enjoying lots of ice and drinks while lounging outside in chairs by a lake. Life was good. But during one of my trips inside to get more ice and a drink, to my horror the Lithium battery was down to 25%. I came in for a drink, and not to have to figure out this damn thing. Shockingly, the inverter was using twenty eight amps! A huge amount of amps was going somewhere. And how long has this been going on? I turned off the refrigerator; And that was it!

Because of Dometic's non regulation of temperature in Manual Mode, I had to leave the refrigerator in Automatic to keep the refrigerator from running all the time. Stupid people! But the problem is that we are boondocking! We do not want to be running the refrigerator on AC; It uses 28 amps.

So, the second problem with Dometic, and I think it is with all Dometics, is that there is no way to specify what power source you want. If in the Automatic Mode, which it needs to be in for temperature regulation, AC takes precedents by default over gas, even if that is not what you want. Evidently Dometic never planned for there trailers to be used in a boondocking scenario with inverters. In a park with full hook ups, AC is generally the choice, and coincidently is the default. But boondocking demands that the batteries never run an absorption type refrigerator! That is insanity! What were they thinking?


Here is a schematic of the DM2652...
There is no problem with the hardware. In red is the 120VAC Heating element. In green is the Gas Heating. There is one other heating circuit which the DM2652 does not have. It is for a Three Way. It is the 12 volt heating element. It is called "K" in the schematic. But I can not imagine why it would ever be used or desireable in an RV. The AC Heater pulls 28 amps from the batteries through an inverter. But this circuit would also pull approximately the same power directly from the batteries. There is no difference. You never want to use batteries on an evaporative refrigerator. Batteries should only be used on a high efficiency compressor type of refrigerator. Three way is just a name dropping vernacular ploy.


Before I get into the solution, here is the back side of the power board. And again... There is nothing wrong with it! The hardware is fine. The problem is stupid people. They live at the factory.


The problem is here. It is here in the fine print. It is casually skipped over, unless you read it. It states that there is no temperature controls if you try to manually select Gas! Part "C" describes the situation that I have observed many times: Freezer temperatures below zero, and frozen food in the refrigerator section. WTF!
Who actually reads this stuff?


That is only part of the problem: the other is high currents when in AC Mode. If you are not boondocking, and you are in a RV Park with full hookups, then there is no problem. Or, at least it is the parks problem, because electricity is usually free in a short term park. Here the refrigerator is pulling 26 amps from the batteries, or almost 300 watts. Why, in anyone's right mind, would they want their batteries drained?

Or why, in anyone's right mind, would they want to run down their gas needlessly 24/7? Because the damn refrigerator is stuck onn, and will not shut off. And that is what will happen if you select Manual-Gas.

And if you want cooling regulation - because it is neat to have - and select Automatic, as in Automatic-AC, your inverter will suck your battery down.

Dometic fixed the problem in latter models, but they did not recall the effected models.

And one more parting shot...
Dometic evidently figured there was no real fire danger to have a refrigerator running continuously in the hot summertime on Manual-Gas.


But I have a solution:
Simply add a switch to kill AC. Simple.
I thought of using a breaker to shut off AC, but that will not work because the refrigerator shares the breaker that goes to all coach outlets. And that makes some sense because the refrigerator plugs into an ordinary outlet just like all the rest. It just happens to be behind the refrigerator. Besides I am not wearing out a breaker by turning it on and off. A breaker is not a switch, and is a stupid Red Neck idea to use it as such.



I have already installed the red led to show me when the refrigerator is onn using gas. Now I want an led to show me when the refrigerator is onn using AC.
Here is an external PNP Bipolar transistor to feed an indicator LED. Happens to be green to contrast with the red LED indicator for the gas flame. This indicator is for the AC 120VAC Heater. The indicator circuit also goes to one of my Microprocessor Boards. From there speech is created for the refrigerator. The PIC can see the two heat sources and enunciate the states.



I have added an extra diode to make sure I get a good voltage drop, about 2 * 0.7 v, from emitter to base. More decisive. You always always have to coat electrical tape with an adhesive coating. All electrical tape will unravel in time.



Not shown is the switch to kill all AC to the refrigerator. Dometic failed to supply this capability on there own.


Here is a picture of the 120VAC Switch. The refrigerator is properly running on inverter 120VAC using 28 amps. Not that this is what you want to do. You should never run a evaporative refrigerator on inverter 120vac, nor on 12vdc; they are exactly the same thing as far as running down coach batteries. Instead use an energy efficient compressor type refrigerator on batteries.



It was supper easy to implement speech. Just a few lines of code that point to speech in another code module, denoted by SPKREONN and SPKREOFF. In the name of brevity, I choose not to send the request to my Event Que. There, all kinds of work or jobs are handled asynchronously, when ever there is time. Assembly does not have such a feature, so I invented it many years ago. Anyway, sorry... This is not the place to talk about the code.

I tested everything with the RV sitting still. Works great. But a real test comes only by having the RV near a lake or an ocean.


I am getting off the subject. Inside the cabinet that has a red glow is one of the Microprocessor boards that I invented. That board contains speech instructions that go to the Speech Microprocessor.




The sign on the refrigerator inside the oval touts "Automatic refrigerator temperature control."
But that is not quite true. Misleading at the best.
Only under "Automatic" is temperature control.




Well, anyway...
The refrigerator regulates now. And, in addition, I can see when it is onn, whether AC or Gas.